This application claims the priority of German patent document 197 32 076.7, filed Jul. 25, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a process for manufacturing a wheel for a motor vehicle by means of friction welding.
From German Patent Document DE-A-44 35 666, a vehicle wheel made of light metal is known which consists of a wheel spider and a rim ring which are connected with one another by means of friction welding. In this case, the wheel spider and/or the rim ring may consist of a magnesium alloy. In practice, it was found that the wheel parts made of a magnesium alloy cannot easily be friction welded. The friction welding parameters, which otherwise apply to light-metal alloys, particularly to aluminum alloys, cannot be transferred to magnesium alloys, at least not while achieving the desired high strengths and reliabilities of the friction welded connection.
It is therefore an object of the present invention to provide a suitable manufacturing process for the friction welding of such wheel parts, of which at least one consists of a magnesium alloy.
This and other objects have been achieved according to the present invention by providing a process for manufacturing a wheel for a motor vehicle, in which a wheel spider and a rim ring are connected with one another by friction welding and at least one of said wheel spider and said rim ring is made of a magnesium alloy, wherein the controlling of the speed of the initial friction, of the friction and of the compression, of the friction welding process takes place as a function of physical characteristics of the magnesium alloy.
According to the invention, the speed of the start of the friction, the frictional speed and compression (upsetting) speed are controlled according to the physical characteristics of the magnesium alloy. These physical characteristics particularly relate to the deformation capacity of the respective aluminum alloy but also to other physical characteristics, such as the melting point, the thermal conductivity, the specific heat or the like. Within dissimilar pairings of material, for example, between an aluminum alloy and a magnesium alloy, the magnesium alloy with its requirements therefore determines the friction welding parameters to be set. In the case of similar pairings of material between two different magnesium alloys, the friction welding parameters are determined by the physical characteristics of the lower-deforming alloys or of the alloy which has the higher melting point and/or the higher thermal conductivity and/or the higher specific heat. According to this process, the components can be friction welded with a high reliability and connection strength. In particular, cracks are avoided on the friction welding connection seams, particularly the outside seam. In addition, generally high stability values are achieved which are uniform on the wheel circumference.
As an alternative to or in combination with the above-mentioned process steps, the required friction welding quality is also achieved by a preheating or additional heating of the wheel part during the friction welding process. This is particularly important for compensating different deformation capacities of the participating magnesium alloy(s). In this case, a heated inert gas may be used for the heating, which has the additional favorable effect that the friction welding area is shielded and oxidation problems, in particular, are avoided.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.